1. Field of the Invention
This invention relates to a polymer filtering apparatus particularly suitable for use in the production of films and fiber of polymers such as polyester, polyamide and the like.
2. Prior Art
When producing fiber or films by extruding a molten polymer through a nozzle or die, it is a matter of upmost importance to remove foreign matter from the polymer in order to obtain a product of satisfactory quality. For this purpose, there have been proposed and used various filters. For instance, there has been known in the art the so-called leaf filter which is constituted by a couple of filter members (hereinafter referred to as "fiber filters") stacked one on the other, each consisting of a thin disk-like metal fiber sinter with an opening at the center thereof, the filter members being secured to each other, for example, by welding outer peripheral portions thereof, a wire netting of a large mesh size interposed between the filter members to form a gap space therebetween, and a porous plate for supporting the fiber filters. A filtering apparatus is formed by stacking a large number of such leaf filters one on another around the circumference of a support column (referred to as "polymer duct") which is centrally provided with a polymer passage. The polymer to be filtered is fed from outside of the leaf filters and passed through the fiber filters to enter the internal gap spaces and sent into the polymer duct through the center openings. During the filtering operation, each fiber filter which is insufficient in rigidity for withstanding the filtration pressure by itself is supported by the porous plate and wire netting.
The leaf filter of the above-described construction has a broad filtration area and employs fiber filters with narrow interstices, so that it is capable of removing foreign matter with high efficiency, and it is widely used in the art. However, such a leaf filter has a number of problems to be solved. Namely, the fiber filter is very costly, and therefore it is desired to be easily washable for repeated use. Nevertheless, a difficulty is encountered in washing the interior of the filter which is closed along its outer periphery. Besides, eye inspection of the filter which is usually required after washing to ascertain the effects of washing, especially inspection of the secondary side of the filter which forms an exit for the polymer, is impossible because it is located on the inner side of the filter. Insufficient washing of the secondary side leaves the possibilities of the dust or other foreign matter on the secondary side mixing into the polymer during the filtering operation.